1. Field of the Invention
The present invention pertains to the field of testing apparatus which provides a simulation of the atmospheric pressure conditions at any selected altitude. While the present invention is designed particularly for the similation of high altitude ambient pressures, the apparatus may also be used for simulating pressures than ambient.
This field of design has become very important recently due to the regulations of various government agencies upon the operating conditions and emissions of automotive internal combustion engines. For example, The Environmental Protection Agency has devised a group of tests under which an internal combustion engine must be certified in order to allow sale thereof. Some of these tests must be performed at high altitude locations such as Denver and other cities located well above sea level. In order to simulate the conditions existing at such high altitude locations, the automotive manufacturers have an immediate need for a simulation device which will provide the characteristics of high altitude operation of a internal combustion engine at the presently existing test locations throughout the United States.
2. Description of the Prior Art
Throughout the last couple of decades, many engine testing devices have been designed to simulate conditions at the various altitudes at which the engines will be operated. These testing devices were designed primarily for use with aeronautical equipment since aircraft engines were the sole concern at that time. Also, the prior art designs were primarily concerned with power and acceleration rather than efficiency and emissions control. Examples of such patents are U.S. Pat. No. 2,357,625 and 2,615,331.
Another pertinent prior art U.S. Pat. No. 1,503,307 issued to Durr on a motor testing chamber. The Durr patent is an example of an early design for simulating ambient pressures at values less than sea level atmospheric pressure. The design utilizes a closed chamber with a single exhausting fan. The exhausting fan is arranged to primarily exhaust from the exhaust manifold of the internal combustion engine and secondarily to selectively draw additional air from the simulated atmosphere within the chamber. The chamber includes an inlet port for admitting air within the chamber which is controlled by a reducing valve therein for limiting passage of air into the chamber. In this manner, pressures may be simulated at values lower than sea level atmospheric pressure. The present invention distinguishes over the Durr patent since Durr throttles upstream only and uses only an exhaust blower while the present invention includes an intake blower and an exhaust blower and throttles at the intake and at the exhaust from the chamber. The Durr design does not cool the exhaust gases returning to the atmosphere within the chamber and therefore does not maintain a constant mass flow. Also the Durr patent does not have a feed back control for maintaining the desired atmospheric conditions under transient operating conditions. Also the Durr design requires the location of the test unit or engine within the simulated environment chamber whereas the present invention allows remote location of the test unit. These and further advantages will be described below.